1. Field of the Invention
The present invention relates to air cleaners used in conjunction with engines. More particularly, the present invention concerns air cleaners which utilize ram air pressure.
2. Description of the Related Art
Japanese Patent Laid-open No. 9-96261 entitled "Air cleaner for vehicles" discloses an air cleaner of the type which utilizes ram air pressure. Such types of air cleaners are well known. With reference to FIGS. 8-10, ram air is introduced into an intake passage 206 and the air having passed through the intake passage 206 enters into a lower case 210 through an inlet 209. The air then passes from the lower case 210 through an element 207. The clean air that has passed through the element 207 is guided into an upper case 208, and introduced into a carburetor 202 connected to a lower portion of the upper case 208. The ram air is utilized to produce a ram pressure higher than the atmospheric pressure. The ram pressure is applied to the carburetor 202 to supply a high-density air-fuel mixture into an engine 201 for thereby increasing the air-fuel mixture charging efficiency of the engine 201 to increase the output power thereof when the vehicle runs at a high speed.
As shown in FIG. 10, the lower case 210 has left and right inlets 209 with respective intake passages 206 connected thereto. The structure of the lower case 210 and the intake passages 206, as shown in FIG. 8, is of a general nature. With the above structure, air flows introduced from the inlets 209 collide with each other in the center of the lower case 210. Though the ram pressure, higher than the atmospheric pressure, is generated utilizing the ram air, a sufficient ram pressure may not be applied to the carburetor 202. Furthermore, the air flows introduced from the inlets 209 develop vortex flows at the bottom or sides of the lower case 210 (As will be discussed in relation to FIG. 7a, hereinafter). When a vortex flow loss is caused, the ram air cannot effectively be introduced into the carburetor 202 because the resistance in the flow passages is increased.